(a) Technical Field
The present invention relates to an active thermal management system for a fuel cell stack. More particularly, the present invention relates to an active thermal management system for a fuel cell stack, which controls the distribution of coolant flow for each unit cell based on the temperature distribution measured at unit cells of the fuel cell stack.
(b) Background Art
A fuel cell system mounted in a fuel cell vehicle includes a fuel cell stack for generating electricity by electrochemical reaction of hydrogen and oxygen, a hydrogen supply system for supplying hydrogen as a fuel to the fuel cell stack, an oxygen (air) supply system for supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, and a thermal management system (TMS) for removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing a water management function.
The thermal management system forms a cooling loop or a heating loop used to circulate coolant based on the temperature of the fuel cell stack.
That is, the thermal management system forms a cooling loop for pumping/circulating low temperature coolant from a radiator to the fuel cell stack during high-temperature operation of the fuel cell stack, and forms a heating loop for pumping/circulating the hot coolant discharged from the fuel cell stack back to the fuel cell stack in order to heat the fuel cell stack during a cold start-up, for example.
As shown in FIG. 1, the coolant circulated by the cooling loop or heating loop is supplied to a coolant inlet manifold 14 of a fuel cell stack 10 to cool unit cells 12 which constitute the fuel cell stack 10, and is then discharged through a coolant outlet manifold 16.
However, temperature variations can occur due to various conditions in the fuel cell stack in which more than several hundreds of unit cells are stacked, and the temperature variations cannot be solved only by uniform distribution of coolant.
For example, referring to the graph of FIG. 2 showing a temperature gradient over the unit cells of the fuel cell stack, there is a temperature gradient within the unit cells located at both ends of the fuel cell stack which are in contact with end plates, and the temperature gradient within the unit cells located in the middle of the fuel cell stack. Further, the temperature gradient in the fuel cells located in the middle of the fuel cell stack is smaller than that of the unit cells at the both ends of the fuel cell stack. For this reason, it is difficult to solve the temperature gradient over the whole unit cells using a uniform distribution of coolant.
As such, there is a temperature variation in the unit cells of the fuel cell stack, and increased temperature variation deteriorates the performance and durability of the fuel cell stack, which is very problematic.
The above information discussed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to persons of ordinary skill in the art.